Low-frequency non-separable transform (LFNST) with reduced zero-out in video coding

ABSTRACT

An example device for decoding video data includes a memory configured to store video data; and one or more processors implemented in circuitry and configured to: determine that a transform block of video data has a size of 8×8 coefficients and that the transform block is transformed using a low-frequency non-separable transform (LFNST); decode at least nine non-zero transform coefficients of the transform block; inverse transform the transform block using an inverse LFNST to reproduce a residual block corresponding to the transform block; and reconstruct a block of the video data using the residual block.

This application claims the benefit of U.S. Provisional Application No.62/951,984, filed Dec. 20, 2019, the entire contents of which are herebyincorporated by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In general, this disclosure describes techniques for transform coding invideo coding, such as in video compression standards. For instance, thisdisclosure describes various examples of low-frequency non-separabletransform designs that may improve coding efficiency. The exampletechniques may be utilized in Versatile Video Coding (VVC/H.266). Theexample techniques may be used with other advanced video codecsincluding extensions of HEVC and the next generation of video codingstandards. In particular, certain techniques of this disclosure relateto explicitly coding (encoding or decoding) certain numbers of non-zerotransform coefficients, and not coding remaining transform coefficients,of an 8×8 transform block that is transformed using a low-frequencynon-separable transform (LFNST). For instance, a video coder may beconfigured to explicitly code up to ten transform coefficients of thetransform block, and the video coder may infer values of zero for theremaining transform coefficients.

In one example, a method of decoding video data includes: determiningthat a transform block of video data has a size of 8×8 coefficients andthat the transform block is transformed using a low-frequencynon-separable transform (LFNST); decoding at least nine non-zerotransform coefficients of the transform block; inverse transforming thetransform block using an inverse LFNST to reproduce a residual blockcorresponding to the transform block; and reconstructing a block of thevideo data using the residual block.

In another example, a device for decoding video data includes a memoryconfigured to store video data; and one or more processors implementedin circuitry and configured to: determine that a transform block of thevideo data has a size of 8×8 coefficients and that the transform blockis transformed using a low-frequency non-separable transform (LFNST);decode at least nine non-zero transform coefficients of the transformblock; inverse transform the transform block using an inverse LFNST toreproduce a residual block corresponding to the transform block; andreconstruct a block of the video data using the residual block.

In another example, a computer-readable storage medium has storedthereon instructions that, when executed, cause a processor to:determine that a transform block of video data has a size of 8×8coefficients and that the transform block is transformed using alow-frequency non-separable transform (LFNST); decode at least ninenon-zero transform coefficients of the transform block; inversetransform the transform block using an inverse LFNST to reproduce aresidual block corresponding to the transform block; and reconstruct ablock of the video data using the residual block.

In another example, a device for decoding video data includes means fordetermining that a transform block of video data has a size of 8×8coefficients and that the transform block is transformed using alow-frequency non-separable transform (LFNST); means for decoding atleast nine non-zero transform coefficients of the transform block; meansfor inverse transforming the transform block using an inverse LFNST toreproduce a residual block corresponding to the transform block; andmeans for reconstructing a block of the video data using the residualblock.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 3 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 4 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 5 is a block diagram illustrating an example set of components thatmay perform Low-Frequency Non-separable Transformation (LFNST).

FIG. 6 is a conceptual diagram illustrating application of an inverseLFNST to a transform block to reproduce a residual block.

FIG. 7 is a conceptual diagram illustrating application of an inverseLFNST to a 4×4 block.

FIG. 8 is a conceptual diagram illustrating application of an inverseLFNST to a 4×4 block to produce an 8×8 block.

FIG. 9 is a flowchart illustrating an example of encoding video dataaccording to the techniques of this disclosure.

FIG. 10 is a flowchart illustrating an example of decoding video dataaccording to the techniques of this disclosure.

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,unencoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch as smartphones, televisions, cameras, display devices, digitalmedia players, video gaming consoles, video streaming device, or thelike. In some cases, source device 102 and destination device 116 may beequipped for wireless communication, and thus may be referred to aswireless communication devices.

In the example of FIG. 1, source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply techniques for low-frequencynon-separable transform (LFNST) with reduced zero-out, as described inthis disclosure. Source device 102 represents an example of a videoencoding device, while destination device 116 represents an example of avideo decoding device. In other examples, a source device and adestination device may include other components or arrangements. Forexample, source device 102 may receive video data from an external videosource, such as an external camera. Likewise, destination device 116 mayinterface with an external display device, rather than include anintegrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forLFNST with reduced zero-out, as described in this disclosure. Sourcedevice 102 and destination device 116 are merely examples of such codingdevices in which source device 102 generates coded video data fortransmission to destination device 116. This disclosure refers to a“coding” device as a device that performs coding (encoding and/ordecoding) of data. Thus, video encoder 200 and video decoder 300represent examples of coding devices and, in particular, a video encoderand a video decoder, respectively. In some examples, source device 102and destination device 116 may operate in a substantially symmetricalmanner such that each of source device 102 and destination device 116includes video encoding and decoding components. Hence, system 100 maysupport one-way or two-way video transmission between source device 102and destination device 116, e.g., for video streaming, video playback,video broadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e.,raw, unencoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some examples, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Insome examples, portions of memories 106, 120 may be allocated as one ormore video buffers, e.g., to store raw, decoded, and/or encoded videodata.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video generated by source device 102. Destination device 116may access stored video data from file server 114 via streaming ordownload. File server 114 may be any type of server device capable ofstoring encoded video data and transmitting that encoded video data tothe destination device 116. File server 114 may represent a web server(e.g., for a website), a File Transfer Protocol (FTP) server, a contentdelivery network device, or a network attached storage (NAS) device.Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. File server 114and input interface 122 may be configured to operate according to astreaming transmission protocol, a download transmission protocol, or acombination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a cathode ray tube(CRT), a liquid crystal display (LCD), a plasma display, an organiclight emitting diode (OLED) display, or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

As described above, one video coding standard is HEVC. HEVC is describedin M. Wien, High Efficiency Video Coding: Coding Tools andSpecification, Springer-Verlag, Berlin, 2015.

Video encoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as the Joint Exploration TestModel (JEM) or ITU-T H.266, also referred to as Versatile Video Coding(VVC). A recent draft of the VVC standard is described in Bross, et al.“Versatile Video Coding (Draft 7),” Joint Video Experts Team (JVET) ofITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 16^(th) Meeting: Geneva,CH, 1-11 Oct. 2019, JVET-P2001-v14 (hereinafter “VVC Draft 7”). Thetechniques of this disclosure, however, are not limited to anyparticular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to JEM or VVC. According to JEM or VVC,a video coder (such as video encoder 200) partitions a picture into aplurality of coding tree units (CTUs). Video encoder 200 may partition aCTU according to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) (also called ternary tree (TT)) partitions. Atriple or ternary tree partition is a partition where a block is splitinto three sub-blocks. In some examples, a triple or ternary treepartition divides a block into three sub-blocks without dividing theoriginal block through the center. The partitioning types in MTT (e.g.,QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in apicture. As one example, a brick may refer to a rectangular region ofCTU rows within a particular tile in a picture. A tile may be arectangular region of CTUs within a particular tile column and aparticular tile row in a picture. A tile column refers to a rectangularregion of CTUs having a height equal to the height of the picture and awidth specified by syntax elements (e.g., such as in a picture parameterset). A tile row refers to a rectangular region of CTUs having a heightspecified by syntax elements (e.g., such as in a picture parameter set)and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, eachof which may include one or more CTU rows within the tile. A tile thatis not partitioned into multiple bricks may also be referred to as abrick. However, a brick that is a true subset of a tile may not bereferred to as a tile.

The bricks in a picture may also be arranged in a slice. A slice may bean integer number of bricks of a picture that may be exclusivelycontained in a single network abstraction layer (NAL) unit. In someexamples, a slice includes either a number of complete tiles or only aconsecutive sequence of complete bricks of one tile.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of JEM and VVC also provide an affine motion compensationmode, which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofJEM and VVC provide sixty-seven intra-prediction modes, includingvarious directional modes, as well as planar mode and DC mode. Ingeneral, video encoder 200 selects an intra-prediction mode thatdescribes neighboring samples to a current block (e.g., a block of a CU)from which to predict samples of the current block. Such samples maygenerally be above, above and to the left, or to the left of the currentblock in the same picture as the current block, assuming video encoder200 codes CTUs and CUs in raster scan order (left to right, top tobottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT)or discrete sine transform (DST), an integer transform, a wavelettransform, or a conceptually similar transform to residual video data.Additionally, video encoder 200 may apply a secondary transformfollowing the first transform, such as a mode-dependent non-separablesecondary transform (MDNSST), a signal dependent transform, aKarhunen-Loeve transform (KLT), a low-frequency non-separable transform(LFNST), or the like. Video encoder 200 produces transform coefficientsfollowing application of the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the transform coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of the transformcoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information of apicture into CTUs, and partitioning of each CTU according to acorresponding partition structure, such as a QTBT structure, to defineCUs of the CTU. The syntax elements may further define prediction andresidual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

In accordance with the techniques of this disclosure, video encoder 200and video decoder 300 may be configured to perform operations related toLFNST. In LFNST, as described in more detail, video encoder 200 mayperform DCT or DST on residual values to generate transform coefficientsand perform LFNST on the resulting transform coefficients of the DCT orDST to generate LFNST coefficients, and then quantize, entropy encode,and signal the LFNST coefficients. In the reciprocal, video decoder 300may receive quantized, entropy encoded LFNST coefficients, and performentropy decoding on the quantized, entropy encoded LFNST coefficientsand inverse quantize the quantized LFNST coefficients to generate LFNSTcoefficients. Video decoder 300 may perform inverse LFNST on the LFNSTcoefficients to generate inverse transformed LFNST coefficients, whichmay be the same as the transform coefficients generated by video encoder200, and perform inverse DCT or DST on the inverse transformed LFNSTcoefficients to generate the residual values of a reconstructed residualblock.

Video encoder 200 may be configured to only explicitly encode a certainnumber of the quantized LFNST coefficients (for brevity, referred tobelow simply as “LFNST coefficients,” but it should be understood thatthe LFNST coefficients may also be quantized). For example, videoencoder 200 may explicitly encode up to ten of the LFNST coefficients.Thus, video encoder 200 may explicitly encode any number in the range[1, 2, . . . , 9, 10] LFNST coefficients of an 8×8 transform block.

Video encoder 200 may determine the number of LFNST coefficients toexplicitly encode using, e.g., a complexity of video data, such as aprofile, tier, and/or level of a video coding standard to which thevideo data conforms. Additionally or alternatively, video encoder 200may determine the number of LFNST coefficient to explicitly encode usinga rate-distortion optimization (RDO) process. In some examples, thenumber of LFNST coefficients to explicitly encode may be predefined,e.g., by an applicable video coding standard.

Video encoder 200 may encode a value representing the number of LFNSTcoefficients that are explicitly encoded, e.g., in a video parameter set(VPS), a sequence parameter set (SPS), a picture parameter set (PPS), anadaptation parameter set (APS), a picture header, a slice header, ablock header, or in other syntax data. Video encoder 200 may avoidencoding values for transform coefficients beyond the number of non-zerotransform coefficients. Video encoder 200 may be configured according toa constraint imposed by a video coding standard that sets a maximumnumber of explicitly coded non-zero LFNST coefficients, e.g., a maximumof ten.

Video decoder 300 may also determine the number of non-zero LFNSTcoefficients of an 8×8 block that are encoded to be in the range [1, 2,. . . , 9, 10]. For example, video decoder 300 may determine the numberto be a predefined (i.e., a predetermined) value or from signaled data,such as a value signaled in a VPS, SPS, PPS, APS, picture header, sliceheader, block header, or other such syntax data. Video decoder 300 maythen decode the number of non-zero LFNST coefficients from a bitstreamincluding the video data, and infer (i.e., without coding) thatremaining transform coefficients (e.g., 64 minus the number of encodedLFNST coefficients) are zero valued. Thus, video decoder 300 maydetermine that encoded video data of the video bitstream following thelast explicitly encoded non-zero LFNST coefficient of the transformblock corresponds to a syntax element other than a transform coefficient(e.g., other than syntax elements representing whether the transformcoefficient is significant, greater than one, greater than two, aremaining level, a sign, or the like).

Thus, in one example, an 8×8 transform block may be transformed usingLFNST and may include nine non-zero explicitly coded transformcoefficients, with fifty-five uncoded transform coefficients that areinferred to have values of zero. That is, the bitstream would notinclude any data for the fifty-five uncoded transform coefficients inthis example. As another example, an 8×8 transform block may betransformed using LFNST and may include ten non-zero explicitly codedtransform coefficients, with fifty-four uncoded transform coefficientsthat are inferred to have values of zero. That is, the bitstream wouldnot include any data for the fifty-four uncoded transform coefficientsin this example.

In this manner, there may be a constraint on the number of non-zerocoefficients that are allowed (e.g., number of non-zero coefficientsafter DCT or DST transform from video encoder 200 or number of non-zerocoefficients in the LFNST coefficients). Having this constraint mayreduce computational overhead for video encoder 200 and video decoder300, which may improve the operation of video encoder 200 and videodecoder 300.

In one example, video encoder 200 may be configured to perform atransform on residual values to generate a TU, determine that the TUsize is 4×4, set all coefficients of the TU except for eightcoefficients equal to zero, perform LFNST on the TU having at most eightnon-zero coefficients to generate LFNST coefficients, and signalinformation indicative of the LFNST coefficients. In one example, videoencoder 200 may be configured to perform a transform on residual valuesto generate a TU, determine that the TU size is 8×8, set allcoefficients of the TU except for ten coefficients equal to zero,perform LFNST on the TU having at most ten non-zero coefficients togenerate LFNST coefficients, and signal information indicative of theLFNST coefficients. In one example, video encoder 200 may be configuredto perform a transform on residual values to generate a TU, determinethat the TU size is greater than 8×8, set all coefficients of the TUexcept for sixteen coefficients equal to zero, perform LFNST on the TUhaving at most sixteen non-zero coefficients to generate LFNSTcoefficients, and signal information indicative of the LFNSTcoefficients.

In one example, video decoder 300 may be configured to generate a TU ofsize 4×4 having a plurality of coefficients, wherein the TU comprises atmost eight non-zero coefficients, perform an inverse LFNST on the TU togenerate inverse transformed LFNST coefficients, perform an inversetransform on the inverse transformed LFNST coefficients to generateresidual values for a current block, and reconstruct the current blockbased on the residual values. In one example, video decoder 300 mayconfigured to generate a TU of size 8×8 having a plurality ofcoefficients, wherein the TU comprises at most ten non-zerocoefficients, perform an inverse LFNST on the TU to generate inversetransformed LFNST coefficients, perform an inverse transform on theinverse transformed LFNST coefficients to generate residual values for acurrent block, and reconstruct the current block based on the residualvalues. In one example, video decoder 300 may configured to generate aTU of size greater than 8×8 having a plurality of coefficients, whereinthe TU comprises at most sixteen non-zero coefficients, perform aninverse LFNST on the TU to generate inverse transformed LFNSTcoefficients, perform an inverse transform on the inverse transformedLFNST coefficients to generate residual values for a current block, andreconstruct the current block based on the residual values.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, because quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 130(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 130 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), then the nodes can befurther partitioned by respective binary trees. The binary treesplitting of one node can be iterated until the nodes resulting from thesplit reach the minimum allowed binary tree leaf node size (MinBTSize)or the maximum allowed binary tree depth (MaxBTDepth). The example ofQTBT structure 130 represents such nodes as having dashed lines forbranches. The binary tree leaf node is referred to as a coding unit(CU), which is used for prediction (e.g., intra-picture or inter-pictureprediction) and transform, without any further partitioning. Asdiscussed above, CUs may also be referred to as “video blocks” or“blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If theleaf quadtree node is 128×128, the leaf quadtree node will not befurther split by the binary tree, because the size exceeds the MaxBTSize(i.e., 64×64, in this example). Otherwise, the leaf quadtree node willbe further partitioned by the binary tree. Therefore, the quadtree leafnode is also the root node for the binary tree and has the binary treedepth as 0. When the binary tree depth reaches MaxBTDepth (4, in thisexample), no further splitting is permitted. When the binary tree nodehas a width equal to MinBTSize (4, in this example), it implies nofurther horizontal splitting is permitted. Similarly, a binary tree nodehaving a height equal to MinBTSize implies no further vertical splittingis permitted for that binary tree node. As noted above, leaf nodes ofthe binary tree are referred to as CUs, and are further processedaccording to prediction and transform without further partitioning.

The following describes transform related tools. In video codingstandards prior to HEVC, only a fixed separable transform is used whereDCT-2 is used both vertically and horizontally. In HEVC, in addition toDCT-2, DST-7 is also employed for 4×4 blocks as a fixed separabletransform.

U.S. Pat. No. 10,306,229, U.S. Patent Publication No. 2018/0020218, andU.S. Patent Publication No. 2019/0373261 describe multiple transformselection (MTS) methods. MTS is previously called Adaptive MultipleTransforms (AMT), which is only a name change and the technique is thesame. An example of MTS in U.S. Patent Publication No. 2019/0373261 hasbeen adopted in the Joint Experimental Model (JEM-7.0) of the JointVideo Experts Team (WET) and later a simplified version of MTS isadopted in VVC.

FIG. 3 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 3 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200 inthe context of video coding standards such as the HEVC video codingstandard and the H.266 video coding standard in development. However,the techniques of this disclosure are not limited to these video codingstandards, and are applicable generally to video encoding and decoding.

In the example of FIG. 3, video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videoencoder 200 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video encoder 200 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 3 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, one or more of the units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1) may store theinstructions (e.g., object code) of the software that video encoder 200receives and executes, or another memory within video encoder 200 (notshown) may store such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,unencoded version of the current block from video data memory 230 andthe prediction block from mode selection unit 202. Residual generationunit 204 calculates sample-by-sample differences between the currentblock and the prediction block. The resulting sample-by-sampledifferences define a residual block for the current block. In someexamples, residual generation unit 204 may also determine differencesbetween sample values in the residual block to generate a residual blockusing residual differential pulse code modulation (RDPCM). In someexamples, residual generation unit 204 may be formed using one or moresubtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder200 and video decoder 300 may also support asymmetric partitioning forPU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as afew examples, mode selection unit 202, via respective units associatedwith the coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a discrete sine transform(DST), a directional transform, a Karhunen-Loeve transform (KLT), or aconceptually similar transform to a residual block. In some examples,transform processing unit 206 may perform multiple transforms to aresidual block, e.g., a primary transform and a secondary transform,such as a rotational transform. In some examples, transform processingunit 206 does not apply transforms to a residual block.

In one or more examples described in this disclosure, transformprocessing unit 206 may include the separable and LFNST blocks labeled“encoder side” in FIG. 5 below. For example, transform processing unit206 may perform a separable transform (e.g., DCT-2) on residual valuesto generate transform coefficients, and then perform LFNST on thetransform coefficients to generate LFNST coefficients. The LFNSTcoefficients may then be quantized and entropy encoded for signaling.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

According to the techniques of this disclosure, entropy encoding unit220 may entropy encode a predetermined number of non-zero LFNSTcoefficients of an 8×8 transform block, e.g., nine or ten LFNSTcoefficients. Entropy encoding unit 220 may determine that a currenttransform block has a size of 8×8 coefficients and was transformed usingan LFNST. Thus, entropy encoding unit 220 may entropy encode thepredetermined number of non-zero LFNST coefficients (e.g., nine or tennon-zero LFNST coefficients), then skip encoding of the remaining LFNSTcoefficients. Inverse transform processing unit 212 may treat theskipped LFNST coefficients as having values of zero.

Entropy encoding unit 220 may be preconfigured with the predeterminednumber of non-zero LFNST coefficients to encode. Alternatively, entropyencoding unit 220 may receive data from, e.g., mode selection unit 202as to the predetermined number. For example, mode selection unit 202 maydetermine rate-distortion optimization (RDO) values for encoding up toten non-zero LFNST coefficients and select the number of non-zero LFNSTcoefficients yielding the best RDO value as the predetermined number.Entropy encoding unit 220 may further be configured with a predeterminedmaximum number of non-zero LFNST coefficients to encode, e.g., ten. Modeselection unit 202 may determine the RDO values during an encodingprocess, e.g., to encode the transform block (as well as a blockcontaining the transform block, e.g., a CU). Additionally oralternatively, mode selection unit 202 may determine the predeterminednumber according to a profile, tier, and/or level of an applicable videocoding standard to which a bitstream including the transform blockconforms. Entropy encoding unit 220 may entropy encode data representingthe predetermined number as well, such as in a VPS, SPS, PPS, APS,picture header, slice header, block header, or other such syntaxstructure.

Thus, in one example, entropy encoding unit 220 may receive an 8×8 blockof LFNST coefficients, i.e., sixty-four (64) total LFNST coefficients.Entropy encoding unit 220 may entropy encode the LFNST coefficients suchthat entropy encoding unit 220 entropy encodes nine or ten non-zeroLFNST coefficients, and skip encoding of the remaining LFNSTcoefficients (sixty-four minus the number of non-zero encoded LFNSTcoefficients, e.g., fifty-five or fifty-four).

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream. The bitstream may conform to an applicable video codingstandard, such as HEVC or VVC, and in particular, may apply to aparticular profile, tier, and/or level combination of the correspondingbitstream.

Inverse transform processing unit 212 may be configured to inversetransform the transform block. For example, inverse transform processingunit 212 may initially determine that only the predetermined number ofLFNST coefficients have non-zero values, and that the remaining LFNSTcoefficients are zero valued. Inverse transform processing unit 212 mayapply an inverse LFNST, then an inverse primary transform, to inversequantized LFNST coefficients received from inverse quantization unit210, to reproduce a residual block. Reconstruction unit 214 mayreconstruct the original block (e.g., original coding block). In thismanner, video encoder 200 may also be considered a device for decodingvideo data, in that video encoder 200 includes a decoding looprepresented by inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, and DPB218.

The operations described above are described with respect to a block ofvideo data. Such description should be understood as being operationsfor a luma coding block and/or chroma coding blocks. As described above,in some examples, the luma coding block and chroma coding blocks areluma and chroma components of a CU. In some examples, the luma codingblock and the chroma coding blocks are luma and chroma components of aPU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding block andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured to performa transform on residual values to generate a TU, determine that the TUsize is 4×4, set all coefficients of the TU except for eightcoefficients equal to zero, perform LFNST on the TU having at most eightnon-zero coefficients to generate LFNST coefficients, and signalinformation indicative of the LFNST coefficients. The one or moreprocessing units implemented in circuitry may be configured to perform atransform on residual values to generate a TU, determine that the TUsize is 8×8, set all coefficients of the TU except for ten coefficientsequal to zero, perform LFNST on the TU having at most ten non-zerocoefficients to generate LFNST coefficients, and signal informationindicative of the LFNST coefficients. The one or more processing unitsimplemented in circuitry may be configured to perform a transform onresidual values to generate a TU, determine that the TU size is greaterthan 8×8, set all coefficients of the TU except for sixteen coefficientsequal to zero, perform LFNST on the TU having at most sixteen non-zerocoefficients to generate LFNST coefficients, and signal informationindicative of the LFNST coefficients.

Video encoder 200 also represents an example of a device for decodingvideo data including a memory configured to store video data; and one ormore processors implemented in circuitry and configured to: determinethat a transform block of the video data has a size of 8×8 coefficientsand that the transform block is transformed using a low-frequencynon-separable transform (LFNST); decode at least nine non-zero transformcoefficients of the transform block; inverse transform the transformblock using an inverse LFNST to reproduce a residual block correspondingto the transform block; and reconstruct a block of the video data usingthe residual block.

FIG. 4 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of JEM, VVC, and HEVC. However, the techniques of thisdisclosure may be performed by video coding devices that are configuredto other video coding standards.

In the example of FIG. 4, video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videodecoder 300 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video decoder 300 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. In other examples, video decoder 300 may include more,fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as DRAM, including SDRAM, MRAM,RRAM, or other types of memory devices. CPB memory 320 and DPB 314 maybe provided by the same memory device or separate memory devices. Invarious examples, CPB memory 320 may be on-chip with other components ofvideo decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 4 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 3, fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, one or more of the units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT or inverse DST,an inverse integer transform, an inverse Karhunen-Loeve transform (KLT),an inverse rotational transform, an inverse directional transform, oranother inverse transform to the transform coefficient block.

In one or more examples described in this disclosure, inverse transformprocessing unit 308 may include the inverse LFNST and inverse separableblocks illustrated in the decoder side of FIG. 5. For example, inversetransform processing unit 308 may receive decoded coefficients (e.g.,decoded LFNST coefficients) and perform inverse LFNST to generateinverse transformed LFNST coefficients (which may be similar or the sameas the transform coefficients generated after the separable transform byvideo encoder 200). Inverse transform processing unit 308 may performinverse separable transform (e.g., DCT-2) to generate the residualvalues.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 3).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 3).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notperformed, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are performed,filter unit 312 may store the filtered reconstructed blocks to DPB 314.As discussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures (e.g.,decoded video) from DPB 314 for subsequent presentation on a displaydevice, such as display device 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a videodecoding device including a memory configured to store video data, andone or more processing units implemented in circuitry and configured togenerate a TU of size 4×4 having a plurality of coefficients, whereinthe TU comprises at most eight non-zero coefficients, perform an inverseLFNST on the TU to generate inverse transformed LFNST coefficients,perform an inverse transform on the inverse transformed LFNSTcoefficients to generate residual values for a current block, andreconstruct the current block based on the residual values. The one ormore processing units implemented in circuitry may be configured togenerate a TU of size 8×8 having a plurality of coefficients, whereinthe TU comprises at most ten non-zero coefficients, perform an inverseLFNST on the TU to generate inverse transformed LFNST coefficients,perform an inverse transform on the inverse transformed LFNSTcoefficients to generate residual values for a current block, andreconstruct the current block based on the residual values. The one ormore processing units implemented in circuitry may be configured togenerate a TU of size greater than 8×8 having a plurality ofcoefficients, wherein the TU comprises at most sixteen non-zerocoefficients, perform an inverse LFNST on the TU to generate inversetransformed LFNST coefficients, perform an inverse transform on theinverse transformed LFNST coefficients to generate residual values for acurrent block, and reconstruct the current block based on the residualvalues.

Video decoder 300 also represents an example of a device for decodingvideo data including a memory configured to store video data; and one ormore processors implemented in circuitry and configured to: determinethat a transform block of the video data has a size of 8×8 coefficientsand that the transform block is transformed using a low-frequencynon-separable transform (LFNST); decode at least nine non-zero transformcoefficients of the transform block; inverse transform the transformblock using an inverse LFNST to reproduce a residual block correspondingto the transform block; and reconstruct a block of the video data usingthe residual block.

FIG. 5 is a block diagram illustrating an example set of components thatmay perform Low-Frequency Non-separable Transformation (LFNST). Theexample of FIG. 5 depicts both encoder and decoder side LFNST. On theencoder side, an encoder, such as video encoder 200, may apply a primary(separable) transform, then an LFNST, then quantize the LFNSTcoefficients. On the decoder side, a decoder, such as video decoder 300,may apply inverse quantization, inverse LFNST, then inverse primary(separable) transform.

LFNST, as illustrated in FIG. 5, is used in JEM-7.0 to further improvethe coding efficiency of MTS. LFNST is previously called non-separablesecondary transform (NSST) or secondary transform where all theseabbreviations refer to the same process. An implementation of LFNST isbased on U.S. Pat. No. 10,448,053. Also, U.S. Pat. No. 10,491,922, U.S.Patent Publication No. 2017/0094314, U.S. Pat. No. 10,349,085, U.S.Provisional Application No. 62/668,105, and U.S. Patent Publication No.2019/0297351 describe alternative designs and further details. Recently,LFNST has been adopted in VVC standard based on Koo et al. “CE6: ReducedSecondary Transform (RST) (CE6-3.1),” Joint Video Experts Team (WET) ofITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 14^(th) Meeting: Geneva,CH, 19-27 Mar. 2019, JVET-N0193 (hereinafter “JVET-N0193”).

FIG. 6 is a conceptual diagram illustrating application of an inverseLFNST to a transform block to reproduce a residual block. The followingdescribes the decoding process with LFNST. The inverse transformationwith LFNST involves following example steps illustrated in FIG. 6. Thedecoded transform coefficients (e.g., subblock 400 in FIG. 6) are usedas input to the inverse LFNST by first converting the 2-D block into a1-D list (or vector) of coefficients via pre-defined scanning/ordering.An inverse LFNST is applied to the 1-D list of input coefficients andthe output coefficients are reorganized into a 2-D block via pre-definedscanning/ordering (e.g., subblock 402 in FIG. 6). The inversetransformed LFNST coefficients are used as input to the separableinverse DCT-2 to obtain reconstructed residuals.

FIG. 7 is a conceptual diagram illustrating application of an inverseLFNST to a 4×4 block. In the current version of VVC Draft 7, LFNST canbe applied to 4×4 and 8×8 subblocks. In both cases, sixteen decodedcoefficients in a 4×4 subblock (some of which may be normativelyzeroed-out) are input to an inverse LFNST. For the 4×4 case, a 16×16inverse LFNST is used to construct sixteen intermediate coefficientsbefore the separable inverse DCT-2 as shown in FIG. 7.

FIG. 8 is a conceptual diagram illustrating application of an inverseLFNST to a 4×4 block to produce an 8×8 block. In particular, in thisexample, the inverse LFNST is used to reconstruct forty-eightintermediate coefficients from sixteen input coefficients, thenrearranging the intermediate coefficients into an L-shaped pattern. Forthe 8×8 case, a 16×48 inverse LFNST is used to construct forty-eightintermediate coefficients before the separable inverse DCT-2 as shown inFIG. 8. In FIG. 8, the forty-eight intermediate coefficients arereorganized in an L-shaped pattern.

An inverse LFNST processes can be fully defined based on (i) a transformmatrix (e.g., LFNST transform matrix) and (ii) a reorganizationpattern/scan for intermediate coefficients. U.S. Provisional ApplicationNo. 62/849,689; describes an example of a zero-out process in VVC Draft7. Another example of grouping ordered list of coefficients withzero-out is described in U.S. Provisional Application No. 62/799,410.

For a 4×4 LFNST, the following two patterns/scans are used depending onintra mode:

  const int g_lfnstRGScan4x4 [16] = { // 0 1 2 3 4 5 6 7 8 9 10 11 12 1314 15  0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 }; const intg_lfnstRGTranScan4x4[16] = { // 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0, 4, 8,12, 1, 5, 9,13, 2, 6, 10, 14, 3, 7, 11, 15 };

In the above, two patterns/scans indicate the reordering of intermediatecoefficients. For example, g_lfnstRGScan4×4 does not change therow-major reordering of coefficients. However, lfnstRGTranScan4×4reorders by transposing the order of coefficients (e.g., coefficients at1,2,3,6,7 and 11 are swapped with coefficients at 4,8,12,9,13 and 14,respectively).

For 4×4 LFNST, the eight 16×16 matrices are used as candidates incurrent VVC. These are listed in Section 8.7.4.3 of JVET-O2001: Bross,et al. “Versatile Video Coding (Draft 6),” Joint Video Experts Team(JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 15^(th)Meeting: Gothenburg, S E, 3-12 Jul. 2019.

For an 8×8 LFNST, the following two patterns/scans are used depending onintra mode:

const int g_lfnstRGScan8x8 [48] = { // 0 1 2 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 3738 39 40 41 42 43 44 45 46 47  0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,31, 32, 33, 34, 35, 40, 41, 42, 43, 48, 49, 50, 51, 56, 57, 58, 59 };const int g_lfnstRGTranScan8x8[48] = { // 0 1 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 3637 38 39 40 41 42 43 44 45 46 47  0, 8, 16, 24, 32, 40, 48, 56, 1, 9,17, 25, 33, 41, 49, 57, 2, 10, 18, 26, 34, 42, 50, 58, 3, 11, 19, 27,35, 43, 51, 59, 4, 12, 20, 28, 5, 13, 21, 29, 6, 14, 22, 30, 7, 15, 23,31 };

In the above, two patterns/scans indicate the reordering of intermediatecoefficients. Specifically, g_lfnstRGScan8×8 reorganizes 48 intermediatecoefficients in the L-shaped pattern (e.g., the 48th coefficient ismapped to location 59 in FIG. 8). The scan lfnstRGTranScan4×4 reordersthe L-shaped pattern by transposing coefficients (e.g., the 48thcoefficient is mapped to location 31 in FIG. 8). For 8×8 LFNST, eight16×48 matrices are used as candidates in current VVC. These are listedin Section 8.7.4.3 of JVET-O2001.

There may be some issues with LFNST techniques. For example, thezeroing-out process may be undesirable unless necessary (e.g., zero-outprocess may be necessary to reduce the worst-case number ofmultiplications to reduce complexity). For the LFNST design in currentVVC, the worst-case number of multiplications per coefficient is equalto 8 (due to the case of 4×4 LFNST applied to 4×4 TUs, where (8×16)/16=8multiplications per coefficient are needed). The second-worst case isdue to the 8×8 LFNST applied to 8×8 TUs, where (8×48)/64=6multiplications per coefficient are needed.

The worst-case may be still maintained in VVC if up to 10 non-zerocoefficients were allowed in 8×8 LFNST (i.e., (10×48)/64=7.5multiplications per coefficients are needed). Accordingly, the number ofunnecessarily zeroed-out coefficients can be reduced by allowing twomore coefficients (e.g., two more non-zero coefficients) in thetransform block. That is, the worst case scenario can allow up to 10non-zero coefficients.

In order to allow at most ten coefficients for the VVC design, thisdisclosure describes the following example techniques that may be usedtogether or separately. If LFNST is used and TU size is 4×4, then atmost eight non-zero coefficients are allowed in the decoded coefficients(e.g., block 400 of FIG. 6), and the rest of the coefficients arenormatively zeroed-out. If LFNST is used and TU size is 8×8, then atmost ten non-zero coefficients are allowed in the decoded coefficients(e.g., block 400 of FIG. 6), and the rest of the coefficients arenormatively zeroed-out. If LFNST is used (e.g., in examples where TUsize is greater than 8×8), then at most sixteen non-zero coefficientsare allowed in the decoded coefficients (e.g., block 400 of FIG. 6), andthe rest of the coefficients are normatively zeroed-out.

Updates to VVC Draft 7 for above example of block size dependentzeroing-out for LFNST can be reflected as follows with <DELETE> and</DELETE> indicating deletion and <ADD> and </ADD> are used to indicateaddition.

-   -   The variables predModeIntra, nLfnstOutSize, log 2LfnstSize,        nLfnstSize, and nonZeroSize are derived as follows:

predModeIntra = ( cIdx = = 0 ) ? IntraPredModeY[ xTbY ][ yTbY ] :IntraPredModeC [ xTbY ] [ yTbY ] (1149) nLfnstOutSize = ( nTbW >= 8 &&nTbH >= 8) ? 48 : 16    (1150) log2LfnstSize = ( nTbW >= 8 && nTbH >= 8) ? 3 : 2     (1151) nLfnstSize = 1 << log2LfnstSize              (1152) <DELETE> nonZeroSize = ( ( nTbW ==4 && nTbH = = 4) | | ( nTbW = =8 && nTbH = = 8 ) ) ? 8 : 16     (1153)</DELETE>  — <ADD> If ( nTbW = =4 && nTbH = = 4 ) is true, the following   applies:        nonZeroSize =8  — Otherwise, if ( nTbW = = 8 && nTbH = = 8 ) is true, the following  applies:              nonZeroSize = 10  — Otherwise, the followingapplies:              nonZeroSize = 16 </ADD>

FIG. 9 is a flowchart illustrating an example method for encoding acurrent block. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 3), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 9.

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. Video encoder 200 may then calculate a residual blockfor the current block (352). To calculate the residual block, videoencoder 200 may calculate a difference between the original, unencodedblock and the prediction block for the current block.

Video encoder 200 may then transform the residual block and quantizetransform coefficients of the residual block (354). In particular,according to the techniques of this disclosure, video encoder 200 mayapply a primary (separable) transform to the residual block, then applyan LFNST to the resulting transformed coefficients to generate LFNSTcoefficients. Video encoder 200 may then quantize the LFNSTcoefficients. Video encoder 200 also determines a number of non-zeroLFNST coefficients to encode (356). For example, video encoder 200 mayperform RDO testing, and/or determine the number of non-zero LFNSTcoefficients according to a profile, tier, and/or level of acorresponding video coding standard to which the video data corresponds.

Next, video encoder 200 may scan the quantized LFNST coefficients (358).During the scan, or following the scan, video encoder 200 may entropyencode the determined number of non-zero LFNST coefficients (360). Forexample, video encoder 200 may encode the LFNST coefficients using CAVLCor CABAC. Furthermore, video encoder 200 may skip encoding of subsequentLFNST coefficients, thereby treating the remaining LFNST coefficients ofthe transform block as having values of zero. Video encoder 200 may thenoutput the entropy encoded data of the block (362).

Video encoder 200 may also inverse quantize and inverse transform theLFNST coefficients (364). In particular, video encoder 200 mayreconstruct a transform block including the predetermined number ofnon-zero LFNST coefficients that were encoded, and zero valuedcoefficients for the remaining coefficients of the transform block. Byinverse transforming the transform block (using an inverse LFNST and aninverse primary/separable transform, video encoder 200 may reproduce theresidual block. Video encoder 200 may then reconstruct an original block(366), e.g., by combining the residual block with the prediction block.

In this manner, the method of FIG. 9 represents an example of a methodof decoding video data including determining that a transform block ofvideo data has a size of 8×8 coefficients and that the transform blockis transformed using a low-frequency non-separable transform (LFNST);decoding at least nine non-zero transform coefficients of the transformblock; inverse transforming the transform block using an inverse LFNSTto reproduce a residual block corresponding to the transform block; andreconstructing a block of the video data using the residual block.

FIG. 10 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and4), it should be understood that other devices may be configured toperform a method similar to that of FIG. 10.

Video decoder 300 may receive entropy encoded data for the currentblock, such as entropy encoded prediction information and entropyencoded data for coefficients of a residual block corresponding to thecurrent block (370). Video decoder 300 may determine a number ofnon-zero LFNST coefficients for the current block (372), assuming thecurrent block includes an 8×8 LFNST transform block.

Video decoder 300 may entropy decode the entropy encoded data todetermine prediction information for the current block and to reproducecoefficients of the residual block (374). While entropy decoding theentropy encoded data, video decoder 300 may entropy decode only thedetermined number of non-zero LFNST coefficients for the current block,e.g., nine or ten non-zero LFNST coefficients.

Video decoder 300 may predict the current block (376), e.g., using anintra- or inter-prediction mode as indicated by the predictioninformation for the current block, to calculate a prediction block forthe current block.

Video decoder 300 may then inverse scan the number of non-zero LFNSTcoefficients (378), to create a transform block of quantized non-zeroLFNST coefficients, and set remaining coefficients in the transformblock equal to zero (380). Video decoder 300 may then inverse quantizeand inverse transform the transform coefficients (using both an inverseLFNST and an inverse primary/separable transform) to produce a residualblock (382). Video decoder 300 may ultimately decode and reconstruct thecurrent block, including combining the prediction block with theresidual block (384).

In this manner, the method of FIG. 10 represents an example of a methodof decoding video data including determining that a transform block ofvideo data has a size of 8×8 coefficients and that the transform blockis transformed using a low-frequency non-separable transform (LFNST);decoding at least nine non-zero transform coefficients of the transformblock; inverse transforming the transform block using an inverse LFNSTto reproduce a residual block corresponding to the transform block; andreconstructing a block of the video data using the residual block.

Certain example techniques of this disclosure are summarized in thefollowing clauses:

Clause 1: A method of decoding video data, the method comprising:generating a transform unit (TU) of size 4×4 having a plurality ofcoefficients, wherein the TU comprises at most eight non-zerocoefficients; performing an inverse low-frequency non-separabletransform (LFNST) on the TU to generate inverse transformed LFNSTcoefficients; performing an inverse transform on the inverse transformedLFNST coefficients to generate residual values for a current block; andreconstructing the current block based on the residual values.

Clause 2: A method of decoding video data, the method comprising:generating a transform unit (TU) of size 8×8 having a plurality ofcoefficients, wherein the TU comprises at most ten non-zerocoefficients; performing an inverse low-frequency non-separabletransform (LFNST) on the TU to generate inverse transformed LFNSTcoefficients; performing an inverse transform on the inverse transformedLFNST coefficients to generate residual values for a current block; andreconstructing the current block based on the residual values.

Clause 3: A method of decoding video data, the method comprising:generating a transform unit (TU) of size greater than 8×8 having aplurality of coefficients, wherein the TU comprises at most sixteennon-zero coefficients; performing an inverse low-frequency non-separabletransform (LFNST) on the TU to generate inverse transformed LFNSTcoefficients; performing an inverse transform on the inverse transformedLFNST coefficients to generate residual values for a current block; andreconstructing the current block based on the residual values.

Clause 4: The method of any of clauses 1-3, wherein the inversetransform comprises a separable inverse transform.

Clause 5: The method of clause 4, wherein the separable inversetransform comprises an inverse discrete cosine transform (DCT)-2.

Clause 6: The method of any combination of clauses 1-5.

Clause 7: A method of encoding video data, the method comprising:performing a transform on residual values to generate a transform unit(TU); determining that the TU size is 4×4; setting all coefficients ofthe TU except for eight coefficients equal to zero such that the TU hasat most eight non-zero coefficients; performing low-frequencynon-separable transform (LFNST) on the TU to generate LFNSTcoefficients; and signaling information indicative of the LFNSTcoefficients.

Clause 8: A method of encoding video data, the method comprising:performing a transform on residual values to generate a transform unit(TU); determining that the TU size is 8×8; setting all coefficients ofthe TU except for ten coefficients equal to zero such that the TU has atmost ten non-zero coefficients; performing low-frequency non-separabletransform (LFNST) on the TU to generate LFNST coefficients; andsignaling information indicative of the LFNST coefficients.

Clause 9: A method of encoding video data, the method comprising:performing a transform on residual values to generate a transform unit(TU); determining that the TU size is greater than 8×8; setting allcoefficients of the TU except for sixteen coefficients equal to zero,such that the TU has at most sixteen non-zero coefficients; performinglow-frequency non-separable transform (LFNST) on the TU to generateLFNST coefficients; and signaling information indicative of the LFNSTcoefficients.

Clause 10: The method of any of clauses 7-9, wherein the transform is aseparable transform.

Clause 11: The method of clause 10, wherein the transform comprises adiscrete cosine transform (DCT)-2.

Clause 12: The method of any combination of clauses 7-11.

Clause 13: A device for decoding video data, the device comprising: amemory configured to store video data; and processing circuitryconfigured to perform the method of any one or combination of clauses1-6.

Clause 14: The device of clause 13, wherein the device further comprisesa display configured to display decoded video data.

Clause 15: A device for encoding video data, the device comprising: amemory configured to store video data; and processing circuitryconfigured to perform the method of any one or combination of clauses7-12.

Clause 16: The device of any of clauses 13-15, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Clause 17: A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform the method of any one or combination of clauses 1-6 or 7-12.

Clause 18: A device for coding video data, the device comprising meansfor performing the method of any one or combination of clauses 1-6 or7-12.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the terms “processor” and “processingcircuitry,” as used herein may refer to any of the foregoing structuresor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: determining that a transform block of video data has a sizeof 8×8 coefficients and that the transform block is transformed using alow-frequency non-separable transform (LFNST); decoding at least ninenon-zero transform coefficients of the transform block; inversetransforming the transform block using an inverse LFNST to reproduce aresidual block corresponding to the transform block; and reconstructinga block of the video data using the residual block.
 2. The method ofclaim 1, wherein decoding the at least nine non-zero transformcoefficients comprises: decoding at most ten non-zero transformcoefficients of the transform block; and inferring that remainingtransform coefficients of the transform block are zero valued withoutdecoding values for the remaining transform coefficients.
 3. The methodof claim 1, wherein the transform block comprises sixty-four totaltransform coefficients, a number of the total transform coefficients arezero-valued, the number of the total transform coefficients that arezero-valued being equal to sixty-four minus a number of the non-zerotransform coefficients, and the number of the total transformcoefficients that are zero-valued being at most fifty-five.
 4. Themethod of claim 1, wherein decoding the at least nine non-zero transformcoefficients comprises decoding at most a predetermined maximum numberof non-zero transform coefficients for the transform block.
 5. Themethod of claim 4, further comprising setting values of remainingtransform coefficients of the transform block equal to zero.
 6. Themethod of claim 4, further comprising decoding a value representing thepredetermined number from at least one of a video parameter set (VPS), asequence parameter set (SPS), a picture parameter set (PPS), a sliceheader, a coding tree unit (CTU) header, or a block header.
 7. Themethod of claim 1, further comprising: encoding the transform blockprior to decoding the transform block; while encoding the transformblock, determining a number of non-zero transform coefficients to encodefor the transform block, the number being nine or ten; and encoding thenumber of non-zero transform coefficients of the transform block withoutencoding other transform coefficients of the transform block.
 8. Themethod of claim 7, wherein determining the number of non-zero transformcoefficients comprises determining the number of non-zero transformcoefficients to be nine or ten according to a profile, tier, or level ofa video coding standard to which the video data conforms.
 9. A devicefor decoding video data, the device comprising: a memory configured tostore video data; and one or more processors implemented in circuitryand configured to: determine that a transform block of the video datahas a size of 8×8 coefficients and that the transform block istransformed using a low-frequency non-separable transform (LFNST);decode at least nine non-zero transform coefficients of the transformblock; inverse transform the transform block using an inverse LFNST toreproduce a residual block corresponding to the transform block; andreconstruct a block of the video data using the residual block.
 10. Thedevice of claim 9, wherein the one or more processors are furtherconfigured to: decode at most ten non-zero transform coefficients of thetransform block; and infer that remaining transform coefficients of thetransform block are zero valued without decoding values for theremaining transform coefficients.
 11. The device of claim 9, wherein thetransform block comprises sixty-four total transform coefficients, anumber of the total transform coefficients are zero-valued, the numberof the total transform coefficients that are zero-valued being equal tosixty-four minus a number of the non-zero transform coefficients, andthe number of the total transform coefficients that are zero-valuedbeing at most fifty-five.
 12. The device of claim 9, wherein the one ormore processors are configured to decode at most a predetermined maximumnumber of non-zero transform coefficients for the transform block. 13.The device of claim 12, wherein the one or more processors are furtherconfigured to set values of remaining transform coefficients of thetransform block equal to zero.
 14. The device of claim 12, wherein theone or more processors are further configured to decode a valuerepresenting the predetermined number from at least one of a videoparameter set (VPS), a sequence parameter set (SPS), a picture parameterset (PPS), a slice header, a coding tree unit (CTU) header, or a blockheader.
 15. The device of claim 9, wherein the one or more processorsare further configured to: encode the transform block prior to decodingthe transform block; while encoding the transform block, determine anumber of non-zero transform coefficients to encode for the transformblock, the number being nine or ten; and encode the number of non-zerotransform coefficients of the transform block without encoding othertransform coefficients of the transform block.
 16. The device of claim9, further comprising a display configured to display the decoded videodata.
 17. The device of claim 9, wherein the device comprises one ormore of a camera, a computer, a mobile device, a broadcast receiverdevice, or a set-top box.
 18. A non-transitory computer-readable storagemedium having stored thereon instructions that, when executed, cause aprocessor to: determine that a transform block of video data has a sizeof 8×8 coefficients and that the transform block is transformed using alow-frequency non-separable transform (LFNST); decode at least ninenon-zero transform coefficients of the transform block; inversetransform the transform block using an inverse LFNST to reproduce aresidual block corresponding to the transform block; and reconstruct ablock of the video data using the residual block.
 19. The non-transitorycomputer-readable storage medium of claim 18, wherein the instructionsthat cause the processor to decode the at least nine non-zero transformcoefficients comprise instructions that cause the processor to: decodeat most ten non-zero transform coefficients of the transform block; andinfer that remaining transform coefficients of the transform block arezero valued without decoding values for the remaining transformcoefficients.
 20. The non-transitory computer-readable storage medium ofclaim 18, wherein the transform block comprises sixty-four totaltransform coefficients, a number of the total transform coefficients arezero-valued, the number of the total transform coefficients that arezero-valued being equal to sixty-four minus a number of the non-zerotransform coefficients, and the number of the total transformcoefficients that are zero-valued being at most fifty-five.
 21. Thenon-transitory computer-readable storage medium of claim 18, wherein theinstructions that cause the processor to decode the at least ninenon-zero transform coefficients comprise instructions that cause theprocessor to decode at most a predetermined maximum number of non-zerotransform coefficients for the transform block.
 22. The non-transitorycomputer-readable storage medium of claim 21, further comprising settingvalues of remaining transform coefficients of the transform block equalto zero.
 23. The non-transitory computer-readable storage medium ofclaim 21, further comprising instructions that cause the processor todecode a value representing the predetermined number from at least oneof a video parameter set (VPS), a sequence parameter set (SPS), apicture parameter set (PPS), a slice header, a coding tree unit (CTU)header, or a block header.
 24. The non-transitory computer-readablestorage medium of claim 18, further comprising instructions that causethe processor to: encode the transform block prior to decoding thetransform block; while encoding the transform block, determine a numberof non-zero transform coefficients to encode for the transform block,the number being nine or ten; and encode the number of non-zerotransform coefficients of the transform block without encoding othertransform coefficients of the transform block.
 25. The non-transitorycomputer-readable storage medium of claim 24, wherein determining thenumber of non-zero transform coefficients comprises determining thenumber of non-zero transform coefficients to be nine or ten according toa profile, tier, or level of a video coding standard to which the videodata conforms.
 26. A device for decoding video data, the devicecomprising: means for determining that a transform block of video datahas a size of 8×8 coefficients and that the transform block istransformed using a low-frequency non-separable transform (LFNST); meansfor decoding at least nine non-zero transform coefficients of thetransform block; means for inverse transforming the transform blockusing an inverse LFNST to reproduce a residual block corresponding tothe transform block; and means for reconstructing a block of the videodata using the residual block.
 27. The device of claim 26, wherein themeans for decoding the at least nine non-zero transform coefficientscomprises: means for decoding at most ten non-zero transformcoefficients of the transform block; and means for inferring thatremaining transform coefficients of the transform block are zero valuedwithout decoding values for the remaining transform coefficients. 28.The device of claim 26, wherein the transform block comprises sixty-fourtotal transform coefficients, a number of the total transformcoefficients are zero-valued, the number of the total transformcoefficients that are zero-valued being equal to sixty-four minus anumber of the non-zero transform coefficients, and the number of thetotal transform coefficients that are zero-valued being at mostfifty-five.
 29. The device of claim 26, wherein the means for decodingthe at least nine non-zero transform coefficients comprises means fordecoding at most a predetermined maximum number of non-zero transformcoefficients for the transform block.
 30. The device of claim 29,further comprising means for setting values of remaining transformcoefficients of the transform block equal to zero.
 31. The device ofclaim 29, further comprising means for decoding a value representing thepredetermined number from at least one of a video parameter set (VPS), asequence parameter set (SPS), a picture parameter set (PPS), a sliceheader, a coding tree unit (CTU) header, or a block header.
 32. Thedevice of claim 26, further comprising: means for encoding the transformblock prior to decoding the transform block; means for determining anumber of non-zero transform coefficients to encode for the transformblock, the number being nine or ten, while encoding the transform block;and means for encoding the number of non-zero transform coefficients ofthe transform block without encoding other transform coefficients of thetransform block.
 33. The device of claim 32, wherein the means fordetermining the number of non-zero transform coefficients comprisesmeans for determining the number of non-zero transform coefficients tobe nine or ten according to a profile, tier, or level of a video codingstandard to which the video data conforms.